Western plane's plastic was maintained with a cleaner/polish that pretty much eliminated scratches, but that was up to the crew chief (elbow grease and time) and the pilot (what he would accept). Gunners often maintained their own plastic. Pictures often show a not so spotless aircraft with sparkling clean and clear windows. Visibility was considered essential, and a tactical advantage.

The Russians open canopies (I'm a recognized expert here - lol) were often times due as much to fumes and heat as their relatively poor quality plastic.